Implement port equality on SendPortSync

tests/html/js_interop_2_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file
 
 library JsInterop2Test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 import 'dart:isolate';
 
 injectSource(code) {
   final script = new ScriptElement();
   script.type = 'text/javascript';
   script.innerHtml = code;
   document.body.nodes.add(script);
 }
 
 var isolateTest = """
   function test(data) {
     if (data == 'sent')
       return 'received';
   }
 
   var port = new ReceivePortSync();
   port.receive(test);
   window.registerPort('test', port.toSendPort());
 """;
 
+var portEqualityTest = """
+  function identity(data) {
+    return data;
+  }
+
+  var port = new ReceivePortSync();
+  port.receive(identity);
+  window.registerPort('identity', port.toSendPort());
+""";
+
 main() {
   useHtmlConfiguration();
 
   test('dart-to-js-ports', () {
     injectSource(isolateTest);
 
     SendPortSync port = window.lookupPort('test');
     var result = port.callSync('sent');
     expect(result, 'received');
 
     result = port.callSync('ignore');
     expect(result, isNull);
   });
+
+  test('port-equality', () {
+    injectSource(portEqualityTest);
+
+    SendPortSync port1 = window.lookupPort('identity');
+    SendPortSync port2 = window.lookupPort('identity');
+    expect(port1, equals(port2));
+
+    SendPortSync port3 = port1.callSync(port2);
+    expect(port3, equals(port2));
+  });
 }